The present invention relates to a method and device for control of an air - fuel intake system for an internal combustion engine, and more specifically relates to a method and device for control of an air - fuel intake system for an internal combustion engine which includes an intake port construction including both direct and helical intake passages, wherein the relative amounts of intake pass through said direct intake passage and said helical intake passage can be varied. In particular, the present invention relates to control of such an air - fuel intake system, in which said control by variation of the relative amounts of intake flow which pass through said direct intake passage and said helical intake passage is performed by a drive means which is actuated by selective supply of vacuum taken from intake manifold vacuum.
The present patent application has been at least partially prepared from material which has been included in Japanese Patent Application No. Sho 59-173008 (1984), which was invented by the same inventors as the present patent application, and the present patent application hereby incorporates the text of that Japanese Patent Application and the claim or claims and the drawings thereof into this specification by reference; a copy is appended to this specification.
There are some types of variable swirl intake port construction for an internal combustion engine, which have been developed by the present inventors and/or their colleagues in the works of the assignee of the present application previously to the development of the present invention, for the inventive concepts of which Japanese patent application Ser. Nos. 56-51149 (published as Japanese Patent Laying-Open Publication No. 57-165629) and 56-120634 (published as Japanese Patent Laying-Open Publication No. 58-23224) were filed previously to the filing of the Japanese Patent Application relating to the present invention of which priority is being claimed in the present application, and for said inventive concepts of which it is known to the present inventors that U.S. patent application Ser. Nos. 341,911 and 404,145 have been filed claiming the priority of the above identified Japanese patent applications, which however it is not hereby intended to admit as prior art to this application except as otherwise required by law. These types of variable swirl intake port construction incorporate two intake passages formed as leading to the port opening past the intake poppet valve into the combustion chamber of the engine, one of said passages leading substantially straight to said opening, and the other leading in a curved or helical path to said opening. The first or the straight one of said intake passages is controlled by an intake control valve mounted at an intermediate position therealong, so that its effective flow resistance is variable; and thus the relative amounts of intake flow which pass through said direct intake passage and said helical intake passage can be varied. In other words, when said intake control valve is closed to the maximum extent (i.e., in general, is fully closed), then a maximum proportion of the intake flow sucked in by the combustion chamber through the intake port construction is sucked in through the helical intake passage and a minimum proportion of said intake flow is sucked in through the straight intake passage, so that as a whole a maximum amount of swirling is imparted to the intake gas sucked into the combustion chamber. On the other hand, when said intake control valve is closed to the minimum extent (i.e., in general, is fully opened), then a minimum proportion of the intake flow sucked in by the combustion chamber through the intake port construction is sucked in through the helical intake passage and a maximum proportion of said intake flow is sucked in through the straight intake passage, so that as a whole a minimum amount of swirling is imparted to the intake gas sucked into the combustion chamber. Such a type of variable swirl intake port construction for an internal combustion engine is schematically shown in portions of FIGS. 1 and 2 of the accompanying drawings, and will be more fully explained in the portion of this specification entitled "DESCRIPTION OF THE PREFERRED EMBODIMENT".
When the intake flow into the combustion chamber of an internal combustion engine is imparted with a strong swirling, as in the above described case when the aforesaid intake control valve in the straight intake passage is closed as far as possible so that most or all of the intake flow of the engine passes through the helical intake passage, then the apparent flame propagation speed is increased, and it is possible to operate the engine with a very lean mixture, i.e. with a high air/fuel ratio. Further, strong intake swirling helps with stable idling of the engine, so that, other things being equal, the idling speed can be set very low, even when the air/fuel ratio of the mixture being supplied to the engine fluctuates somewhat. On the other hand, the intake volumetric efficiency is reduced, especially during relatively high engine load operation. But in the case when no or very little intake swirling is provided, as in the above described case when the aforesaid intake control valve in the straight intake passage is opened as far as possible so as to combine the flow through said straight intake passage with the flow through the helical intake passage, then the apparent flame propagation speed in the combustion chamber is lower and the engine cannot be operated on mixture of such a low air/fuel ratio, and the idling speed cannot be set so low and the idling is not so stable, but on the other hand the intake volumetric efficiency is much higher. Thus, in the above-identified previous applications, a general form of control method for the intake control valve has been to close it in the engine operational region from low to medium load, so as to substantially eliminate flow through said straight intake passage and to concentrate flow in said helical intake passage and so as to provide high swirling for the gases entering the combustion chamber, whereby in the low to medium load engine operational state the engine can be operated on a very high air/fuel ratio of about 18 to 20 or so--close to the maximum combustible air/fuel ratio; while on the other hand in the engine operational region from medium to high load it has been practiced to provide low swirling for the gases entering the combustion chamber by opening said intake control valve, so as to promote flow through said straight intake passage while reducing the amount of flow through said helical intake passage, and so as to increase volumetric efficiency, while of course the air/fuel ratio cannot be so high (i.e. lean) in this high engine load operational region.
Now, this basic form of control method for the intake control valve as described above has the advantages as just outlined, but, in the case that the intake control valve which controls the above division of the intake gases between the two intake passages is selectively moved to and fro by a vacuum actuator which operates according to selective supply of vacuum thereto, which is a very suitable and typical way for moving such an intake control valve due to the effectiveness of vacuum actuation, and in view of the fact that said vacuum is typically supplied from the intake manifold of the vehicle, the following shortcomings can occur.
In view of the fact that in the low engine load operating condition requiring the intake control valve to be closed a sufficiently great intake manifold vacuum is in general obtainable in the engine intake system, as compared with the generally contrary case in the high engine load operating condition, usually and conventionally it has been practiced to close the intake control valve (so as substantially to interrupt flow through said straight intake passage) by supplying its said vacuum actuator with the intake manifold vacuum, when the value of said vacuum in the intake manifold is greater than a certain vacuum value, in other words when the absolute pressure value in said intake manifold is below a certain absolute pressure value, and conversely to open the intake control valve (so as substantially to freely allow flow through said straight intake passage) by supplying its said vacuum actuator with air at atmospheric pressure, when the value of the vacuum in the intake manifold is less than said certain vacuum value, in other words when the absolute pressure value in said intake manifold is greater than said certain absolute pressure value. This form of control may for example be preformed by an electronic control device including a microcomputer. However, in order to produce a low level of harmful emissions in the exhaust gases of the engine, and in order for the engine to have good fuel economy, it is in fact desirable to operate the engine with high intake swirl, i.e. with the intake control valve closed so as to interrupt flow through the straight intake passage, over as wide a throttle opening range as practicable, and to this end sometimes it is desired for the intake control valve to be maintained as closed, even when the throttle valve has opened so far as to cause the intake manifold vacuum value to drop to such a low level as not properly to be able to keep said intake control valve in the closed state by being supplied to its vacuum actuator. To overcome this difficulty of possible lack of proper actuating vacuum in a certain operational range, it could be conceived of to provide a one way valve in the conduit which leads supply of vacuum to said vacuum actuator, so that, when the intake manifold vacuum value drops as engine load increased, this drop in intake manifold vacuum value is not transmitted to the diaphragm actuator; in other words, an actuating vacuum of sufficiently high vacuum value would be trapped in the diaphragm chamber of the diaphragm actuator, even when the throttle opening amount was so great that adequate vacuum for keeping the intake control valve was not actually available in the intake manifold, until said vacuum was intentionally released to the atmosphere by admission of air at atmospheric pressure into said disphragm chamber when it was definitely desired to open said intake control valve as throttle opening increased over a predetermined value. However, this conceivable solution is not by any means a fully satisfactory one, because of the following considerations. If from the high engine load condition with the intake control valve open the engine load drops until the throttle opening drops below said predetermined value, thereby producing an intake control valve closing command, nevertheless at this time a sufficient value of intake manifold vacuum for closing said intake control valve may not be available, and thereby the intake control valve may not be closed and accordingly the aforesaid intake control valve closing may not be properly obeyed. Such failure to obey an intake control valve closing command, apart from causing trouble by itself by not providing proper intake swirl in circumstances where it is desired, can have the following further troublesome consequences. If the control of the air/fuel ratio of the air - fuel mixture of the engine is being performed by taking into account the position of the intake control valve, which typically in such a control system as outlined above will be the case and may conveniently be being performed by the same microcomputer control system, then it will happen that, even though the intake control valve is not closed so as to produce high swirl in the combustion chamber, an air - fuel mixture of close to the maximum air/fuel ratio usable when the intake control valve is actually closed will be supplied to the engine, and in these circumstances in such absence of swirl there is a great risk of misfiring of the engine occurring. This can lead to severe loss of engine performance. Further, if the control of the ignition timing of the engine is similarly being performed by taking into account the valve opening and valve closing commands for the intake control valve, which again typically in such a system as outlined above may well be the case, then it will happen that proper ignition timing control fails--specifically the ignition timing may become drastically delayed from the proper timing--and again there is a great risk of severe loss of engine performance in these circumstances, as well as loss of drivability.
In other words, to be somewhat metaphorical, the primary problem is that the commands of the control device (such as a microcomputer) for the closing of the intake control valve are in the above outlined circumstances not properly obeyed, due to a lack of supply of vacuum for closingly moving said intake control valve, and this in itself is an undesirable thing; but a secondary, and more troublesome, problem is that despite this disobeying of the commands of the control device said control device thinks that its commands have in fact been obeyed and thinks that now the intake control valve has been closed, and based upon that assumption issues other orders relating to weakening of the air/fuel ratio of the air-fuel mixture and also relating to retardation of the ignition timing, which would be appropriate if the valve were closed but in fact are grossly inappropriate since it is not in fact closed, and, since these further orders are properly obeyed although the earlier valve closing order was not obeyed, much more serious consequences ensue.